This invention relates to information displaying medium and more particularly, to reversible information displaying medium which may be used as a rewritable paper, a displaying sheet for OHP, the displaying section of a magnetic card and the displaying section of an IC card.
Recently, a very large amount of paper and plastic has been used for displaying or recording information, which would cause various problems in resources and environments. Furthermore, information recording cards have been developed for various uses or purposes and thus information recording cards having displaying performance are required. The displaying section of cards and the like is preferably repeatedly writable and erasable so that disused information may be erased and instead necessary information are written. Moreover, displaying medium having security so that displayed information may not easily be rewritten are required.
Displaying medium which are repeatedly writable and erasable include reversible thermal displaying medium comprising a high-polymer matrix and an organic low molecular compound dispersed therein so that scattering and transmission of light may be controlled by controlling heat to be applied for display, displaying medium comprising a film having a plurality of high-polymers blended together so that phase separation may be controlled by heat for display, reversible thermal recording medium using a leuco pigment and a developer, and magnetic recording medium comprising micro-capsules containing dispersing agents in solid state at normal temperature and magnetic powder dispersed therein so that magnetic powder may be moved to the upper portion or the lower portion of the capsule by magnetic field applied under heating for display.
Information displaying medium which utilize change in orientation of liquid crystal material have been proposed, which are superior to the methods mentioned above on visibility and durability. Among method employing low molecular liquid crystal materials there has been proposed a displaying element comprising liquid crystal/high polymer composite film wherein liquid crystal molecules exist in high polymer matrix.
Moreover, a system employing high-molecular liquid crystal memorizing display and having film production performance has been proposed. High polymer liquid crystal is one wherein molecules (mesogen) presenting the nature of liquid crystal are chemically bound to the side chains of high molecular polymer skeleton through a flexing group, whereby settlement of liquid crystal phase is easily made at a temperature lower than glass transformation temperature Tg. Japanese Patent Application Publication Tokkai-sho 63-191673 discloses an example employing such a high-molecular liquid crystal. In the reversible displaying medium as disclosed in the publication, scattering of light under liquid crystal domain state and transmission of light under isotropic liquid state are controlled by controlling heat to be applied for display.
Furthermore, Japanese Patent Application Publication Tokkai-sho 59-10930 discloses an information recording medium which utilizes changes in orientation when heat and electric field is applied to high-molecular liquid crystal or when heat is applied to high-molecular liquid crystal. Also, Japanese Patent Application Publication Tokkai-hei 2-219861 discloses a method of improving a response speed by using a ferroelectrics high-molecular liquid crystal. Japanese Patent Application Publications Tokkai-hei 4-110925 and Tokkai-hei 6-265861 discloses a method of improving a response speed by adding nematic liquid crystal to high-molecular liquid crystal to form smectic phase.
However, conventional systems of displaying element employing liquid crystal/high polymer composite film as mentioned above have problems that a large amount of high polymer material is required for formation of liquid crystal recording layer and that in case of adding dichromatic pigment or the like to be used as host-guest system, diffusion of dichromatic pigment into high polymer material deteriorates contrast.
Moreover, the method as disclosed in Tokkai-sho 63-191673 has problems that slow change of orientation to isotropic liquid state or microscopically dispersed liquid crystal domain state at a temperature higher than Tg of high-molecular liquid crystal necessitates annealing process, thereby resulting in taking a longer time for rewriting.
Moreover, the information recording medium of Tokkai-sho 59-10930 has a problem that speed of orientation in simple high-molecular liquid crystal is very low, not suitable for practical use. Also, the method of Tokkai-hei 2-219861 has problems that orientation process is required when ferroelectrics liquid crystal is used and chiral agent needs to be introduced into high-molecular liquid crystal, thereby resulting in difficulty in synthesizing and high cost. Moreover, the methods as disclosed in Tokkai-hei 4-110925 and Tokkai-hei 6-265861 have a problem that smectic phase changes in orientation according to pressure, thereby resulting in deteriorating durability and conservativity or storability.
Moreover, in these methods, formation or erasing of image is easily made by means of a single energy, thereby resulting in easy tampering of the contents of display.
Under the circumstances mentioned above, there is a strong demand for the advent of an information displaying medium having the following features: they can be used as a rewritable paper, a displaying sheet for OHP, the displaying section of a magnetic card and the displaying section of an IC card; contrast is not deteriorated even if used for a long period or repeatedly used; contrast is not deteriorated due to pressure applied; and they have good conservativity, durability, visibility and resistant to tampering in use at high temperature.
Therefore, an object of this invention is to provide a reversible information displaying medium having such features as mentioned above and a non-contact IC card utilizing such reversible information displaying medium.
According to one aspect of the present invention, the present reversible information display medium of liquid crystal type comprises a recording layer comprising (1) a liquid crystalline composition whose main component exhibits a glass state at room temperature and (2) a dichroic dye, the liquid crystalline composition exhibiting an isotropic liquid state or a liquid crystal domain state by the application of heat and further exhibiting a homeotropic orientation state by the application of both heat and electric field, the formation of letters, images and the like by the application of heat and the elimination thereof by the application of heat and electrical field being able to be carried out, and the images being able to be retained at room temperature even when the application of heat and electrical field is cut.
According to one embodiment of the present invention, the present liquid crystal composition is a high-molecular polymer liquid crystal.
According to one embodiment of the present invention, the high-molecular liquid crystal has a side chain represented by the following general formula (1): 
wherein
rings A, B, C and D independently represent an aromatic or aliphatic hydrocarbon 6 membered ring or a heterocyclic or fused ring;
Z, Z1, Z2 and Z3 independently represent a single bond, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94CFxe2x95x90CFxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
R1 represents a hydrogen atom, a C1-8 straight or branched chain alkyl, alkoxy, alkoxyalkyl or fluoroalkyl group, a cyano group, a halogen atom, a carboxyl group or a hydroxyl group;
X1 and X2 each independently represents a hydrogen atom, a halogen atom or a cyano group;
l is 1 to 20;
m is 0 or 1;
n, p, q and r are independently 0 to 2; and
n+p+q+rxe2x89xa71.
According to another embodiment of the present invention, the present liquid crystal composition is a mixture of a high-molecular liquid crystal and low-molecular liquid crystal.
According to one embodiment of the present invention, the low-molecular liquid crystal is represented by the following general formula (2): 
wherein
Y1 represents a hydrogen atom or a C1-8 straight or branched chain alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl, alkanoyloxy or alkoxycarbonyl group;
rings E and F independently represent a benzene, cyclohexane, cyclohexene, pyrimidine or dioxane ring;
W1 and W2 independently represent a single bond, xe2x80x94CH2Oxe2x80x94, xe2x80x94OCH2xe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CH2xe2x80x94, xe2x80x94CH2CH2xe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94 or xe2x80x94Cxe2x89xa1Cxe2x80x94;
Y represents a hydrogen or halogen atom;
Y2 represents a cyano group, a halogen atom, a C1-8 straight or branched chain alkyl, alkoxy, alkenyl, alkenyloxy, alkoxyalkyl or alkanoyloxy group or a cyano group;
Y3 represents a hydrogen atom, a halogen atom or a cyano group; and
m is 0 to 2.
According to a preferred embodiment of this invention, the contents of said low-molecular liquid crystal in said liquid crystal composition is 30% by weight or below of said high-molecular liquid crystal.
According to another embodiment of this invention, said recording layer is formed on an electrically conductive substrate.
According to another embodiment of this invention, said electrically conductive substrate is transparent and a reflecting layer or a white color layer is formed on the bottom surface of substrate through an air layer.
According to another embodiment of this invention, said recording layer is formed on an electrically conductive layer formed on a substrate.
According to another embodiment of this invention, said substrate and said electrically conductive layer are transparent and a reflecting layer or a white color layer is formed on the bottom surface of said substrate through an air layer.
According to another embodiment of this invention, said electrically conductive layer is transparent, an air layer is provided between said substrate and said electrically conductive layer, and a reflecting layer or a white color layer is formed on the top surface of said substrate.
According to another embodiment of this invention, an ultraviolet rays absorbing layer or a protective layer is formed on said recording layer.
According to a preferred embodiment of the invention, fluorine surface-active agent of 5% by weight of said liquid crystal composition is contained in said recording layer.
According to a preferred embodiment of this invention, high polymer resin of 20% by weight or below of said liquid crystal composition is contained in said recording layer.
According to a preferred embodiment of this invention, filler of 20% by weight or below of said liquid crystal composition is contained in said recording layer.
According to a preferred embodiment of this invention, ultraviolet rays absorbing agent is contained in said recording layer.
According to another aspect of this invention, there is provided a non-contact IC card comprising a rewritable information displaying section utilizing a liquid crystal type reversible information displaying medium as mentioned above and an antenna section coupled to an IC tip section.
According to one embodiment of this invention, the area of the electrically conductive layer or the metallic reflecting layer of said information displaying section is equal to or smaller than 50% of the area of said card.
According to another embodiment of this invention, the electrically conductive layer or the metallic reflecting layer of said information displaying section is divided into two or more regions, and the area of each of said regions is equal to or smaller than 50% of the area of said card.